I think the thing that frustrates me the most isn't the bugs themselves. After all, in general for OSS I'm not paying anyone to make or fix things, and they owe me nothing.

What irritates me is when high-profile projects like Chrome and Firefox (coincidentally both browsers, but that's not my point) then promote themselves as serious, professional-standard projects that people can rely on. They and their evangelists take great pride in stealing market share from established closed source/commercial alternatives (IE in the browser case). Then normal people start using them, expecting a better experience. But then every time there's an update, we play the "will my software even still work?" lottery. (And this applies not just to the browsers, in that example, but also to all the web apps running on them, for which users might be paying real money.)

Unfortunately, on the kinds of geek-friendly forums where these movements tend to start before they expand to the general population, it's often sacrilege to criticise a favoured OSS project. You may get hostile replies, or simply voted into obscurity by whatever mechanism is in place, even if like jwz you take the time to cite specific problems or have provided detailed bug reports and test cases. (Doing the latter is absurdly difficult for many of the large projects anyway, but it gives them a convenient excuse to ignore problems.)

Again, it's completely up to these projects whether to promote helpful contributions or to be hostile. They're giving their stuff away, and owe the rest of us nothing. But it would be nice if there was a little truth in advertising. If an OSS project isn't going to take bug fixing or regression testing seriously, it shouldn't promote itself as professional standard software. (And if a project is created/maintained entirely by one amazingly generous person running the whole show but who has limited time to devote to the project and can't keep up with everything, it would be helpful if there was a prominent warning to that effect somewhere people considering that project would find it before they started relying on it unwisely. Perhaps that would even prompt more concrete support and/or contributions to help the project out.)